Project Summary/Abstract The proposed effort addresses an unmet need for early diagnosis of peripheral artery disease (PAD). PAD is a disorder of vascular circulation that affects more than 8 million Americans, most of whom are unaware of its existence, risks, and threats. PAD is caused primarily by plaque-induced atherosclerosis and in some instances by blood vessel inflammation, stenosis, and injury to the limbs. It is a debilitating, underdiagnosed, undertreated, and poorly understood complication in many diseases including diabetes, sleep apnea and metabolic syndrome. Patients with PAD are 3 to 6 times more likely to have a heart attack or stroke than are patients without PAD. People with PAD have impaired function, including those who are asymptomatic, and experience a significant decline in lower-extremity functioning over time, often leading to critical limb ischemia (CLI), heart attack, and stroke. PAD is difficult to detect in the early stages, requires expensive equipment and trained technicians to diagnose and frequently goes undetected until irreversible tissue damage has occurred. This highlights the need for a simple, inexpensive screening method that can be used to routinely screen those at risk for PAD, including smokers, diabetics and patients with elevated plasma cholesterol. Recent observations indicate that plasma H2S levels are lowered by arterial occlusions and maintaining an adequate level of H2S can be beneficial for preventing atherosclerosis, improving recovery from muscle ischemia and in mitigating damage from myocardial infarction. There are currently few methods to accurately measure plasma H2S and all require specialized equipment, trained technicians and none is non-invasive. In, the proposed study, we intend to demonstrate the feasibility in development of an innovative non-invasive blood H2S measurement device and protocols based on gas-phase electrocatalysis of H2S molecules. In this STTR Phase I study, Exhalix will collaborate with the University of New Mexico, School of Medicine, to perform laboratory animal studies in which the plasma levels of intravenously administered H2S in male Sprague-Dawley rats will be compared to the readings from this diagnostic approach for validation. Plasma samples will be collected from venous lines for analysis in the HPLC-based assays, to determine the threshold, sensitivity and reproducability of the instrument readings. We anticipate that these studies will last approximately 12 months, and success in feasibility demonstration is expected to lead to a Phase II effort for development of an advanced prototype and human studies.